Operation of paper mills



Patented Oct. 22, 1929 I UNITED STATES PATENT OFFICE noNALn K. PATTILLO, or FULTON, ANn JAMEs'n. MAGMAHON, F NIAGARA EALLs,

NEW YoRK, AssIoNo s, BY DIRECT AND M sNE ASSIGNMENTS, To THE MATHIEsoN .ALKALI WORKS, INC, OF NEW YORK, N. Y., A CORPORATION or VIRGINIA OPERATION OF PAPER MILLS 1Y0 Drawing.

This invention relates to improvements in the operation of paper mills.

In paper mill operation considerable loss occurs in the so-called white water discharged 5 from the mill; and the slime problem is one of the serious problems met with in paper mill operation. 1

The present invention provides an v1mproved process in which the losses in the white water are largely eliminated and 1n which a valuable product is recoveredfrom the white water having improved properties and advantages. Our investigation of the slime problem in paper mill operation indicatesthat slimes are due to bacterial action and that different classes of bacterial growths should be distinguished. Certain slimes are caused by bacterial growths or algaeous growths 1n the water supply, while others are due to bacterial growth, for the most part putrefact ve and pathogenic, in the raw matenals, which may at times be supplemented by the algaeous growthiin the raw materials. Pitches or in beating engines and subsequent stock chests differ from slime in that they aredenser and usually of a much darker color and for themost part contain sulfides. They have the characteristics. of a dehydrated slime. We have found that the paper making operation can be benefited by a regulated chlorine treatment of the stock prior to the paper making operation, and that the stock can be effectively sterilized and the slime problem overcomeby such treatment; and that the white water from such paper making opera tion can advantageously be coagulated to give an improved product of stable and sterilized character which can be stored and kept without undergoing objectionable decompxqtion.

According to the present invention e subject the pulp or stock at some point in the mill prior to the paper making operation to the action of chlorine in regulated amount so beater gum which form for the most part x Application filed Deeember- 23, 1927. Serial No. 242,159i.

that there willbe a small but definite residual chlorine content in the water of the treated stock or pulp. Thereby we eflectively sterilize the stock from which the paper is made. 'Where water is added to the stock subsequent to the chlorine treatmentthe water is also sterilized by treatment'with chlorine so that it will also have a small but definitecontent of residual chlorine. This preliminary chlorine treatment benefits the paper making opthen be separated from the white water andobtained for example in the form of laps on a wet machine, which can be stored" in a wet state or dried for shipment. The productso obtained is in a sterile condition and therefore it can be stored and kept without objectionable decomposition such as accompanies coagulated products produced from white water according to methods heretofore proposed. The new coagulated and recovered *product is therefore a superior product of a stable character and can be stored and shipped, either in an undried or in a dried state, and subsequently employed for purposes for which it is adapted.

The white water from which the coagulated material has been separated is itself in a sterile condition and can be used over again to a greater or less extent as mill water in the further operation of the mill.

The sterilization of the pulp or stock prior to the paper making operation can be carried out in different ways and at different points in the paper mill OPGIfitlOIl- With certain pulp, such as ground wood pulp or sulfite pulp, the pulp is advantageously subjected to a preliminary chlorine treatment so as to leave in it a small residual chlorine content which will cause the pulp to be sterilized before it enters the paper mill. WVith other stocks the treatment can be carried out in the paper mill itself. In general, the chlorine treatment should be such as will sterilize the water and destroy sl'me forming bacteria without attacking the es to an objectionable extent. r A

\Ve have found that thesterilization of the "stock can advantageously be effected at a point of high dilution of the stock, such as in the mixing box ahead of the pa er machine. In the mixing box the pulp is highly diluted with water and contains only around 1% or less of actual pulp. In such a diluted stock the chlorine will effectively sterilize the stock without attacking the fibres.

The chlorine treatment of the stock can'be carried out with gaseous chlorine introduced directly into the stock or with the introduction of chlorine water or a solution of hypochlorous acid or a hypochlorite. A particularly advantageous method of introducing the chlorine is by combining the chlorine contiliuously with water in regulated amount and introducing the chlorinated water into the stock.

The chlorination is advantageously elfected continuously by adding a regulated stream residual of chlorine water to the pulp flowing through the mixing box. The amount of chlorine should be such as will give a residual chlorine conte t in the stock or fibre-watermixture of aroun one-half part to one part per million of water as determined by the standard orthotolidine test of the American Public Health Association. Where raw water is added to the showers to dilute the pulp it should also be chlorinated so as to leave a similar chlorine content therein. The amount of chlorine required for the chlorination will vary with different stocks'and different raw water supplies, but it can-readily be regulatedby testin for residual chlorine contentand insuring t e presence of residual Difi'erent coagulating materials can be em ployed, either singly or in combination, for treating the whitewater. Among the coagu lating materials may be mentioned alum,

alum and sodium aluminate, alum and caus-.

tic soda, ferric chloride, etc. The amount of coagulating material needed can readily be determined b testing a sample of the white water with tl ie coagulant. WVe have found around-two pounds of alum per thousand tive coagulation. This value. canreadily be a controlled by controlling the character and amount of the coagulant or the amount of residual chlorine present or by adding electrolytes of suitable character. The white water obtained from stock treated with chlorine as hereinbefore described and having a residual chlorine content of around one-half part to one part per million is in a condition well adapted for coagulation. In white water which we have coagulated' we have found a pH value of around 5.5 to 6.5 most eflective for the coagulation and that the coagulation is more effective in the presence-of a small amount of residual chlorine which appears to serve as a catalyst in promoting the coagulation.

' The coagulated product is advantageously separated from the white water on a wet ma-- chine or a similarmachine. Although the coagulated material is largely, of a-colloidal character it can nevertheless e readily-separated from the white water on a wet machine and obtained in the form of laps similar to laps of ordinary pulp produced on a wet machine, and the laps can be stored and kept in a wet state or dfied to a greater or less extent, particularly in case of shipment.

The new coagulated product, because of its stable and sterible character, can be used either at the same mill where it is formed or shipped toother mills. Because of its content of short fibres and of coaguiated colloid material it is well adapted for use in admixture with longer fibre stock in making certain grades of paper. It can, for example, be

added to the beater or to some other point in the fiow of the stock through the paper mill and in that way admixed with the stock so that it will form part of the paper subsequently produced on the paper machine. For certain grades of paper the presence of the coagulated material is desirable. The separate product-ion of-this coagulated material enables it to be blended and used on certain grades of stock when these are being manufactured while for other stocks in which it is undesirable or less valuable it can be omitted. Its stable and sterile character perfor the particular grades of paper for which it is best suited. In this respect the new coagulated product has important advantages over. unsterilized and unstable coagulated products which deteriorate rapidly and which cannot be stored or kept for any considerable time.

Where the paper being manhfactured continuously on the paper machine is paper in which the coagulated material can advanta-' geously be incorporated itmay -be returned directly from the coagulating and separating step to the stock going throu h the mill. The coagulated material separat on the wet machine may, for example, be passed to the beater and there incorporated with the other fibres which go to make up the stock for the paper machine. In this way the coagulated -material is continuously recovered and in- By treating the white water in this way and obtaining a slime free, stable, coagulated product and returning it and incorporating, it with the stock flowing through the mill the total amount of paper produced. can be considerably increased and the loss of paper stock in the white water greatly reduced.

The white water, asabove stated, is of a sterile character and can advantageously be returned to the mixing boxor to the heater and used in the further operation of the mill,

thus giving to a greater'or less extent a closed cycle of operations and reducing the amount of fresh water required for the mill operation; The sterile character of the white water so returned makes unnecessary the addition of furtherchlorine to sterilize it, thus further economizing in the amount of chlorine required for insuring sterile stockgoing to the paper making machine.

It will thus be seen that the present invenvtion provides an improved method of operating a paper mill in which losses in theJWhite water are eliminated or greatly reduced and in which the material recovered from the white water in a coagulated state is in a stable and sterile condition, well adapted for use in.

the production of paper. It will further be seen that the process includes improvements in the production of paper and in the operation of the paper mill such that trouble from slime is prevented or reduced to an unobjectionable extent.

We 'Elaim:

1. The improvement in the operation of paper mills which comprises subjecting the stock prior to the paper making operation to treatment with chlorine to sterilize the stock, formin paper from the sterilized stock,- and su jecting the white water from such paper making operation to coagulation and recovering the coagulated product in the form of a. stable, sterilized product.

2. The improvement in the operation of .of the white water so that paper mills which comprises subjecting the stock before it goes to the paper making machine to treatment with chlorine to give a stock having a residual chlorine content of about 0.5 to 1 part per million in the fibrewater mixture going to the paper machine, forming paper from the treated stock, and

subjectlng the white water therefrom to coagulation to form a stable, coagulated product and recovering the coagulated product from the white water. J

3. The improvement in the operation of paper mills which comprises subjecting the stock beforeit goes to the. paper machine to treatment with chlorine to give a sterilized stock, forming paper therefrom, subjecting the resulting white water to coagulation to separate therefrom a stable, coagulated, slime-free product and returning the separated product to the stock in the manufacture of paper in the mill.

4. The improvementin the treatment of white water which comprises forming a white water having a residual chlorine content of about 0.5 to 1 part per million, subjecting such white water to coagulation to give a stable, sterilized product, and separating the coagulated productfrom the white water.

-5. The improvement in the treatment of white water which comprises subjecting white water having a residual chlorine content of about 0.5 to 1 part permillion to a coagulating treatment.

6. The improvement in the treatment of white water which comprises subjecting white water having a residual 'chlorine content of about 0.5 to lip'art per million to coagulation with regulation of the pH value the pH value is around 5 to 6. a

7. The improv ement in the operation of paper mills which comprises subjecting white water having a residual chlorine content of about 0.5 to 1 to coagulation, separating the coagulated material from the white water, adding the coagulated material to other pulp -to form the stock flowing to the paper machine, and forming paper from the resulting stock containing such coagulated material.

recovered by coagulation of slime-free white water.

10. As a new product a stable, sterilized, short fibre-containing, coagulated product recovered by coagulation of chlorine-containing white water, such product being of 'a,

5 stable character and having a residual chrine content.

lntestlmony whereof we aflixcur slgnatures.

DONALD K. 'PA'I'IILLO. JAMES H. MAGMAHON. 

